The present invention relates to an improved feeding, sensing and counting system particularly adapted to count with a low degree of error (0.0001) a high rate of randomly-flowing discreet, solid particular material. In particular, the system incorporating the present invention is adapted to count solid objects such as pharmaceutical tablets. Whereas commonly assigned U.S. Pat. No. 3,760,166 is essentially concerned with the sensing and counting techniques of such a system, the instant invention is principally directed to the feeding aspects of this technology.
High-speed feeding and counting of large numbers of discreet, solid particular objects have long presented a problem of counting accuracy to the art. The basic method utilized in the art for sensing/counting employs a light beam disposed across the path of the object and directed towards a sensing means. Each passage of an object across the light beam results in interruption of the beam causing a unique signal to be produced in the sensing means which is used to trigger an appropriate type of counter.
As higher and higher flow rates are attempted, difficulty is experienced in accurately sensing the objects to be counted due to the inability of the device to separate the objects in the flow streams. For example, when tablets of the type used in the pharmaceutical industry are to be counted and are introduced in free fall through a counting channel at high flow rates (5-10 units per second), the tablets tend to come together with no separation. This results in a situation where a unique signature pulse may not be obtained for each individual tablet. It appears that under these circumstances the probability of erroneous signatures occurring is approximately 0.002. This level is unacceptable under new standards of accountability as to pharmaceutical products, which require a counting error of less than one part in 10.sup.4.
Of equal importance in the overall process is a feeding mechanism which can keep up with the speeds contemplated for a multi-channel electronic sensing mechanism. It is necessary for such a feeding arrangement to be able to derandomize objects which are usually introduced in a continuous loading mode such as via a high-volume conveyor arrangement, into a preferred discreet orientation for high-speed accurate handling by the sensing mechanism. High-speed, multi-channel sensor/counter arrangements, moreover, usually require that the objects be presented for sensing in single file and in the orientation most suitable for easy passage through the sensing channel and least likely to cause a jam-up. State of the art arrangements do not reveal a unitary feeding mechanism capable of meeting these requirements.